European Patent Disclosure EP 0 601 228 B1 has disclosed a device for detecting rotations of a shaft which, for example, is an armature shaft of an electric motor of a window lifter or sliding sunroof adjuster. The device in this case is comprised of an essentially hollow, cylindrical magnet body, which as a result of its magnetization, acts as a magnet wheel, and at least one stationary sensor, in this instance a Hall sensor for example, which is disposed resting at a minimum distance from the magnet body. Sometimes an induction coil, for example, can be used instead of a Hall sensor. For example, the hollow magnet body is made of magnetizable particles that are available in the form of powder and a bonding of thermoplastic material. In this instance, the percentage of powder made up of magnetizable particles is chosen to be as great as possible so that the hollow magnet body formed using the injection molding process on the one hand permits the clearest possible signals to be triggered in the sensor, but on the other hand is disadvantageously brittle as a result. Therefore the magnet body is given an inner diameter which, in combination with the diameter of the shaft, produces a sliding seat and the magnet body is glued to the shaft. It must be viewed as disadvantageous that the glue contains solvents and/or other chemicals and requires a disadvantageously long time to harden, for which purpose the glue may possibly also have to be irradiated with ultraviolet light.
European Patent Disclosure EP 0 601 228 B1 also teaches the avoidance of gluing the hollow magnet body to the shaft through the use of a securing piece, which, paired with the shaft, constitutes a press fit pairing and is designed for the transmission of torque from the shaft to the hollow magnet body. In this instance, the transmission takes place through positively engaging means. To this end, the securing piece is embodied, for example, as essentially annular with axially protruding, resilient arms which have hooks on their free ends and extend through grooves provided in the hollow magnet body. This securing piece is injection molded in one piece out of thermoplastic material together with the arms and the hooks. This has the advantage that in the event of a movement of the securing piece on the shaft occurring under pressure, the danger of a damage to the surface of the shaft is slight. A surface of this kind can therefore also constitute a slide pairing, for example, with a sintered bronze coating. Another exemplary embodiment has an annular disk made of metal, e.g. brass, as a first securing piece, which is fixed to the shaft by means of a press-fitting, and a second securing piece which, as a sheet metal part with elastic securing arms, serves to couple the hollow magnet body, which is provided with longitudinal grooves of the outside, to the annular disk. According to the European Patent Disclosure EP 0 611 228 B1, a hollow magnet body and its associated, at least one securing body can be preassembled into one structural unit and can be slid as a structural unit onto the shaft and press-fitted.
The hollow magnet body according to the invention, has an advantage that despite the rigidity of the material used, the magnet body can be pressed onto the shaft carrying the magnet body in order to produce a frictional connection between the shaft and the hollow magnet body. As a result, the annular auxiliary body which encompasses the magnet body in the vicinity of the press pairing protects the hollow magnet body from splitting. Furthermore, with this construction, it is also advantageous that the material which slides when the hollow magnet body is being pressed on, thanks to its thermoplastic bonding, stresses and jeopardizes the surface of the shaft less than an annular disk made of metal according to the prior art. Therefore, the shaft can advantageously have one and the same diameter for receiving the hollow magnet body and for being supported in a slide bearing bush, as a result of which the shaft can be inexpensively manufactured.
Advantageous improvements and updates of the hollow magnet body are possible by means of the measures taken.
The features set forth produce an advantage that despite the disposition of the annular auxiliary body, a lot of end face area is available for the pressing-on of the hollow magnet body, even if the longitudinal section of the hollow magnet body encompassed by the annular auxiliary body is embodied as relatively thin-walled for the sake of improved radial elasticity.
Other features set forth produce an exemplary embodiment in which the hollow magnet body and the annular auxiliary body as well can be manufactured separately in order to be subsequently united with one another.
Still other features produce a advantage that the longitudinal section of the hollow magnet body enclosed by the annular auxiliary body is particularly well-suited in the radial direction for producing the radial press fit with the shaft.
Characterizing features set forth produce an advantage that the annular auxiliary body and the hollow magnet body constitute a combined piece that can be produced in an injection mold and can be slid and press-fitted onto the shaft.
Still other features of claim 6 produce an advantage of an improved positional fixing of the hollow magnet body on the shaft, even with varying operating temperatures.